Renal tubule Na,K-ATPase polarity in glucocorticoid-induced polycystic kidney disease.

Cyst formation in polycystic kidney disease (PKD) involves proliferation of cyst lining epithelial and changes in trans-epithelial fluid and electrolyte transport. In vitro studies have suggested that mislocation of Na,K-ATPase to the apical tubular surface may be an important component of cyst fluid transport. We undertook in vivo studies of Na,K-ATPase location using the "threshold" murine model of glucocorticoid-induced PKD (GIPKD). Using histological, immunohistochemical, and densitometric techniques, we compared cyst formation and the cellular location of Na,K-ATPase in suckling C3H (low threshold for GIPKD) and DBA (high threshold) mice given an inducing dose of 200 mg/kg methylprednisolone acetate. As expected, C3H mice demonstrated greater cyst formation as measured by proportion of section area occupied by the tubule lumen (26.7% vs 15.5%; p < 0.001). Cyst formation was associated with increased Na,K-ATPase staining and increased apical Na,K-ATPase location. MPA treatment in C3H mice resulted in apical staining that exceeded basolateral staining (35.3% of reference window vs 29.8%; p < 0.001). The relatively GIPKD-resistant DBA mice did not show such change in Na,K-ATPase location. These immunohistochemical studies suggest a role for Na,K-ATPase in renal cyst formation.

Renal tubule Na,K-ATPase polarity in different animal models of polycystic kidney disease.

Apical mislocation of the ubiquitous transport enzyme Na,K-ATPase has been implicated as a feature of cyst development in in vitro studies of human polycystic kidney disease (PKD) epithelia. We undertook an immunohistochemical study of murine glucocorticoid-induced PKD, the pcy mouse, the cpk mouse, and the diphenylthiazole (DPT)-induced rat models of PKD to determine if this feature was common to these models of cyst development. Distribution of Na,K-ATPase was determined with a polyclonal anti-Na,K-ATPase antibody and a nickel-silver-enhanced peroxidase color development system. Results were documented objectively with densitometric techniques. Control animals appropriate to the age, strain, and species of the experimental groups demonstrated the expected polar distribution of Na,K-ATPase to the basolateral surface. This distribution was more marked in mature animals. Tubular dilatation and cystic change, however, were associated with increased apical Na,K-ATPase in all models. The murine models demonstrated decreased basolateral staining for Na,K-ATPase compared with controls, although this was not a feature of the DPT rat model. Abnormal location of Na,K-ATPase is a shared feature of a variety of animal models and human PKD. This may contribute to abnormal fluid and electrolyte flux favoring cyst formation or may represent expression of a less differentiated renal tubule epithelial phenotype.

Effect of dietary soy protein and genistein on disease progression in mice with polycystic kidney disease.

The effects of feeding a soy protein isolate or genistein, an isoflavonoid present in soy protein, on cyst development were examined in the DBA/2FG-pcy (pcy) mouse, an accepted animal model of polycystic kidney disease, before the appearance of clinical symptoms. In study 1, 60-day-old male pcy mice were evenly divided into two groups and fed semipurified diets, based on casein or a soy protein isolate (15 g protein/100 g diet) for 90 days. In study 2, the animals were fed a casein-based diet (25 g casein/100 g diet) with or without genistein (0.05 g/100 g diet) for 60 days. In study 1, total kidney weight and kidney weight relative to body weight were significantly reduced (by 24% to 25%) in the animals fed the soy protein-based diet, relative to the casein-fed group, as was kidney water content (by 38%). In addition, mean cyst volume, as measured by morphometry, were lower (by 25%) in kidneys from the soy protein-fed group. No differences were found between these two groups with respect to final body weight, plasma creatinine, and protein content; however, plasma urea values were significantly lower in the soy protein-fed animals. Genistein supplementation of a casein-based diet in study 2 did not reduce the renal enlargement and cyst development associated with progression of polycystic kidney disease. These results suggest that soy protein is effective in retarding cyst development in the pcy mouse and that this beneficial effect may be unrelated to its genistein content.

Ontogeny of dexamethasone binding and sodium potassium ATPase activity in experimental murine polycystic kidney disease.

The induction of polycystic kidney disease (PKD) by glucocorticoids in newborn mice behaves as a "threshold" trait, with prevalence of PKD varying in different inbred strains after exposure to an inducing steroid. C3H mice (low threshold for PKD) demonstrated greater specific dexamethasone binding than DBA mice (high threshold) on the second day of life. Treatment with methylprednisolone acetate (MPA), a cyst-inducing steroid, down regulated dexamethasone binding earlier than in DBA mice. C3H mice demonstrated greater whole kidney homogenate Na-K ATPase activity than DBA mice within 24h of MPA injection. Specific renal glucocorticoid binding may be a regulator of threshold for murine glucocorticoid induced PKD. Our findings support in vitro evidence that glucocorticoid induced Na-K ATPase activity during critical periods of nephron development is an important regulatory point of this model.

Increased renal fibrosis and expression of renal phosphatidylinositol 4-kinase-beta and phospholipase C(gamma1) proteins in piglets exposed to ochratoxin-A.

Endemic nephropathy has been linked to exposure of ochratoxin-A (OA) in grains and animal products. The underlying events surrounding this form of renal injury are not well known, partly due to the lack of a suitable animal model of the disease. Therefore, in this study, a pig model of OA-induced renal injury was established and used to examine whether elements of the phosphoinositide signalling pathway are altered in this disease. Weanling piglets were fed diets containing 0, 2, and 4 ppm OA for 6 weeks. Serum creatinine and urea and renal fibrosis were monitored biweekly using serial blood samples and renal biopsies. At termination, the protein levels of renal phosphatidylinositol 4-kinase-beta (PtdIns4Kbeta) and phospholipase C(gamma1) (PLC(gamma1)) were determined using immunoblotting and scanning densitometry. Serum creatinine was elevated by 2 weeks and renal fibrosis was elevated by 4 weeks at both levels of inclusion of OA. At the end of the experimental period, kidney size and water content were elevated, as were the protein levels of renal PtdIns4Kbeta and PLC(gamma1) in OA-exposed animals. Therefore, serial biopsies can be used to track changes in renal pathology in the OA-exposed piglet. We conclude that this is a useful model for OA-induced renal injury in which the underlying molecular events associated with this form of renal injury can be studied.

Immunohistochemical detection of epidermal growth factor in glycol methacrylate embedded tissue.

This study addresses a variety of immunohistochemical conditions for detecting EGF in 3.5% paraformaldehyde fixed, glycol methacrylate embedded tissue including antigen unmasking with trypsin, dilution of primary antibody, and incubation time with primary antibody. Color development was achieved with a biotinylated secondary antibody linked to an avidin biotinylated peroxidase complex. Trypsinization and a 12 hr incubation with the primary antibody was essential to detect EGF in this system. Adequate staining could be achieved with a 1:100 dilution of the primary antibody.

Polycystic kidney disease--a truly pediatric problem.

Polycystic kidney disease (PKD) represents the most common inherited cause of chronic renal failure. PKD is a relatively uncommon cause of chronic renal failure or mortality in childhood and adolescence, but is nevertheless often responsible for symptoms of renal disease. Current research into the pathogenesis of PKD suggests that disturbance of the normal regulation of growth and development of tubular epithelium is intrinsic to cyst formation and growth. Features of cystic epithelium that are analogous to earlier stages of renal development include altered composition of the extracellular matrix, abnormal cell proliferation, and the persistence of a secretory pattern of fluid and electrolyte transport. The potential for early diagnosis and intervention in PKD makes it an area of great interest to the pediatric nephrologist. Animal and in vitro studies have achieved modification of cyst growth by reduction of dietary protein, use of amiloride and its analogs, antagonism of the epidermal growth factor receptor system, anti-inflammatory therapy, and most recently with the use of taxol, an agent that inhibits microtubule assembly. PKD may represent an area in which childhood diagnosis and intervention will have a significant impact on the prevalence of chronic renal failure in adult life.

The use of a eutectic mixture of local anesthetic in pediatric renal biopsy.

Eight children undergoing percutaneous renal biopsy had eutectic mixture of local anesthetic (EMLA) cream substituted for dermal infiltration of local anesthetic. Five children reported no sensation of the initial skin puncture and only one child reported feeling a sharp object. EMLA cream may form a useful part of pediatric renal biopsy.

Glucocorticoid teratogenesis in the developing nephron.

Although the induction of polycystic kidney disease by neonatal glucocorticoid treatment has been extensively documented, there are no data on induction of polycystic kidney disease with fetal exposure to glucocorticoids. We injected groups of pregnant Swiss Webster albino mice subcutaneously with 250 mg/kg of hydrocortisone acetate on individual days from days 1 to 19 of gestation. A control group received an equal volume of saline. Histologic analysis of 1,522 kidneys from the offspring of these animals revealed no evidence of polycystic kidneys in the control group or in offspring of animals injected before day 11 of pregnancy. A bimodal distribution of cystic kidney disease was noted in the remaining animals, with highest prevalence after injection on day 12 (50.8%) and day 17 (34.3%). We conclude that 250 mg/kg of glucocorticoids may induce polycystic kidney disease in utero, but possibly only during critical periods of metanephric development.

Late development of airway obstruction in the Robin anomalad (Pierre Robin syndrome) in the newborn.

A survey of the records of 26 consecutive cases of the Robin anomalad, admitted in the first year of life, was undertaken to review the time at which airway obstruction was first noted to occur after birth. Sixteen cases required active treatment for episodes of airway obstruction associated with cyanosis. Of these, 11 developed obstruction on the first day of life, but five did not obstruct until later (3-21 days). Two infants, both from the early presentation group, died as a result of airway obstruction at 13 and 95 days of age. Management techniques varied over the 11 year period studied, and included prone nursing, body frame, naso-tracheal intubation, nasopharyngeal intubation, and lip tongue anastamosis. Tracheostomy was not performed on any case. There is a significant risk of major airway embarrassment in this disorder (16 of 25, 62%) even if the infant seems initially well (five of 26, 18%). Early management of infants with the Robin anomalad should, therefore, be undertaken at centres where skilled airway support is available.

Transforming growth factor alpha and epidermal growth factor expression in experimental murine polycystic kidney disease.

Cystic change in polycystic kidney disease (PKD) is associated with epithelial hyperplasia, altered fluid and electrolyte transport, and de-differentiation of renal tubular epithelium. The role of polypeptide growth factors as potential modulators of cystic change remains an area of controversy. In this study, the expression of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) were assessed by immunohistochemistry and image analysis in glucocorticoid-induced PKD in the newborn mouse. Newborn C3H mice received either 200 mg/kg methylprednisolone acetate (MPA) or 0.9% saline as a control. EGF expression was not detected in significant quantities in either MPA-treated or control animals. TGF alpha, however, was expressed in immature control kidney in a largely basolateral distribution. Expression increased significantly in association with cystic change in MPA-treated animals and was localized to the apical cell surface, implying altered polarity of secretion. There is no evidence that EGF is a mitogen in this early developmental model of PKD. TGF alpha, however, may be an important mediator of cystic change in immature or de-differentiated renal tubular epithelium.

Amelioration of polycystic kidney disease by modification of dietary protein intake in the rat.

Polycystic kidney disease is the most common potentially lethal single- gene inherited disease in man. There is no specific therapy. Previous studies in the pcy mouse model of polycystic kidney disease have shown amelioration of cystic change by reduction in dietary protein intake. The Han:SPRD-cy rat is a model of autosomal dominant polycystic kidney disease that closely resembles human disease in its histology and clinical course. We compared the morphometric assessment of cystic change and standard laboratory measures of renal function in heterozygous Han: SPRD-cy rats that received isocaloric diets containing either 8% or 20% protein as casein. This level of dietary protein restriction was associated with a significant reduction of mean body weight in the 8% protein group (358 g) compared with 20% protein (490 g; P = 0.027). Mean renal volume, adjusted for the difference in body weight, was significantly lower in the 8% protein group (6.2 mL/kg) compared with the 20% protein group (11.6 mL/kg; P = 0.016). The major component in this reduction was a reduction in total cyst volume to a mean 0.47 mL in the 8% protein group from 2.68 mL in the 20% protein group (P < 0.0001). All 8% protein diet animals survived to 6 months of age, but 3 of 11 20% protein diet animals died between 5 and 6 months of age. Mean serum creatinine and urea levels were significantly lower in the 8% protein group (118 mmol/L and 15.6 mmol/L) compared with the 20% protein group (272 mmol/L, P = 0.0033, and 81.5 mmol/L, P = 0.0002, respectively). Dietary protein restriction is a potent method for modifying the course of polycystic kidney disease in the Han:SPRD-cy/+ rat. These findings emphasize the potential for diet to alter the physiology of the renal tubulointerstitium.

Investigation of pediatric hypertension. Use of a tailored protocol.

Using a comprehensive protocol, the efficacy of simple clinical data, including history, physical examination, and urinalysis, in the discrimination of essential or secondary hypertension was investigated by a review of 103 patients, aged 2 weeks to 18 years, consecutively referred for investigation. Essential hypertension (55/103 mm Hg) was the most common diagnosis, even in infancy, whereas various renal disorders formed the next most common diagnostic category (21/103 mm Hg). Family history and the presence of "fixed" vs "labile" hypertension were of no value in detecting secondary hypertension. Urinalysis was useful in detecting inflammatory renal lesions but not structural disorders of the kidney. This study emphasizes the need for thorough investigation, including renal imaging, of asymptomatic hypertensive children and suggests a useful protocol to achieve this end.

Pediatric renal biopsy in the ambulatory care environment.

The use of pediatric ambulatory care facilities to perform invasive procedures that have low morbidity is increasingly popular. Over a 2-year period, 46 pediatric renal biopsies were performed in an ambulatory care setting at the Winnipeg Children's Hospital, with the patient discharged the same day. There was no serious complications and adequate tissue was obtained in 45 cases. Renal biopsy may be safely performed on an outpatient basis on carefully selected patients by experienced operators in properly equipped facilities.

Na-K ATPase activity in murine glucocorticoid induced polycystic kidney disease in vivo.

The prevalence and severity of polycystic kidney disease (PKD) induced by glucocorticoids in mice can be predicted by a mathematical "threshold" model. We studied the relationship between Na-K ATPase activity and cyst formation in C3H (low threshold for PKD) and DBA mice (high threshold). There was no difference in Na-K ATPase induction by 200 mg/kg methyl prednisolone acetate (MPA) (C3H; 97.4 nmol NADH/min/mg protein: DBA; 94.2 nmol NADH/min/mg protein). C3H mice demonstrated greater cyst formation than DBA animals as measured by area (20.1% relative area vs 13.9%, p < 0.05) or by calculated volume (7.4% relative volume vs 2.3%, p < 0.001). Significant relationships were seen between Na-K ATPase activity and logarithmically transformed area data in C3H animals and with cyst volume in both strains. Na-K ATPase activity is related to cyst formation in glucocorticoid induced PKD, but the level of Na-K ATPase activity is not a determinant of the threshold for glucocorticoid induced PKD.

Deferoxamine and aluminum clearance in pediatric hemodialysis patients.

Mobilization of aluminum by deferoxamine and the subsequent clearance from plasma by hemodialysis with or without charcoal hemofiltration was studied in four pediatric patients. Deferoxamine, 10-20 mg/kg, followed by dialysis with a Travenol CA50 dialyzer produced reductions in mean plasma aluminum levels from 2433 +/- 729 nmol/l (65.5 +/- 19.6 micrograms/l) to 1727 +/- 554 nmol/l (46.5 +/- 14.9 micrograms/l) during dialysis. The use of a charcoal cartridge in the circuit resulted in a reduction in mean plasma aluminum levels 2459 +/- 591 nmol/l (66.2 +/- 15.9 micrograms/ml) to 1380 +/- 106 nmol/l (35.8 +/- 2.9 micrograms/l). In one patient, high-flux dialysis produced a reduction from 2140 nmol/l (55.6 micrograms/l) to 1134 nmol/l (29.4 micrograms/l). No patients suffered direct adverse reactions to low-dose deferoxamine, although two patients had previously exhibited potential aluminum neurotoxicity after rapid increases in plasma aluminum levels with deferoxamine in higher doses. Aluminum levels must be monitored closely during deferoxamine therapy in uremic children to minimize the risk of exacerbating aluminum neurotoxicity.

Cilazapril delays progression of hypertension and uremia in rat polycystic kidney disease.

Polycystic kidney disease (PKD) is the fourth most common cause of end-stage renal disease and is a common cause of hypertension and associated vascular morbidity. Activity of the renin angiotensin system has been identified as a major component of hypertension and altered fluid and electrolyte physiology in PKD. Activity of this pathway also has been proposed as a potential modulator of structural change in both tubules and the interstitium of the kidney. Cilazapril is a long-acting angiotensin-converting enzyme inhibitor that has been effective in producing vascular remodelling in hypertensive vascular disease. We undertook a study to determine whether therapy with cilazapril would modify the expression of PKD in the Han:SPRD-cy rat, a model of autosomal dominant PKD that closely resembles human disease. Male rats were treated for 4 months, starting at 1 month of age. Control animals were hypertensive by 3 months of age, whereas treated animals were noted to be hypertensive only at the exit assessment (P < 0.001 at 3 months, P = 0.005 at 5 months). At 5 months of age, cilazapril-treated animals had modest but statistically significant reductions in serum creatinine (mean, 1.77 mg/dL v 1.97 mg/dL; P = 0.0006) and morphometrically assessed cyst volume (mean, 0.32 mL v 0.67 mL; P = 0.036). Cilazapril is an effective treatment for hypertension in this model of progressive renal disease and may have benefits beyond the prevention of cardiovascular morbidity.

Excess prevalence of non diabetic renal disease in native American children in Manitoba.

We undertook a 1-year prospective point prevalence study to test the hypothesis that there is an excess of non-diabetic renal disease in native American children; 29.6% (73/247) of the population attending the only regional pediatric nephrology clinic in 1993 were native compared with 8.2% of the Manitoba population in this age group (odds ratio = 4.4, P < 0.001). Patients were classified as low risk (normal renal function, no deterioration expected), high risk (normal renal function, deterioration probable), or established chronic renal failure (creatinine clearance chronically low or post renal transplant). Patients were further classified as suffering from congenital renal anomalies, genetic or metabolic disease, or acquired renal disease. Odds ratios were calculated based on data from the Aboriginal Peoples' Population Survey and Statistics Canada census data. The odds ratios for low-risk renal disease, high-risk renal disease, and chronic renal failure were 3.8, 5.6, and 6.3, respectively (P < 0.001 in all categories). The odds ratios for congenital, genetic, or acquired disease were 4.5 (P < 0.001), 0.9 (P = ns), and 6.1 (P < 0.001), respectively. Native American children in Manitoba demonstrate increased prevalence of serious congenital and acquired renal disease. These children are also more likely to live in medically underserviced communities, long distances from tertiary care centers. This study emphasizes the importance of considering factors other than diabetes mellitus when considering the problem of renal disease in native Americans.